1. Technical Field
This invention relates to the art of making ceramic cylinder heads.
2. Description of the Prior Art
As described in a 1987 article, entitled "Adiabatic Diesel Engine Development at Ford Motor Company", by Havstad et al, the desire to achieve an adiabatic engine has brought with it a technical evolution in the use of structural ceramics. Structural ceramics are to be differentiated from ceramics used in catalyst substrates, electronic substrates and china, principally on the basis that they are strong in compression and have moderately high strength in tension. Ceramics are traditionally stable at high temperatures, maintaining high hardness, stiffness and resistance to corrosion. An adiabatic engine is one which operates at consistently high temperatures without a cooling system. Such an engine achieves work through variations in pressure and volume with little heat transfer.
Thin ceramic films or coatings have been used on metal engine components to achieve the introduction of ceramics in an adiabatic engine. This has evolved into the use of thicker ceramic inserts or linings, which are cast in place in the supporting structural metal component or attached in some other satisfactory manner (see Japanese patent 122765; U.S. Pat. No. 599,496 is an exception to this evolutionary trend since as early as 1898, porcelain, not a structural ceramic, was used as a forerunner of such ceramic liners). The last evolutionary stage is to eliminate substantially structural metal, using ceramic as the primary structural member.
Turning specifically to the cylinder head component design, we find that the same evolutionary transition has been taking place. The cylinder head is used herein to mean that member which primarily forms the roof of a combustion chamber and secondarily provides passages for ingress and egress of gases or fluids through such roof for the combustion chamber. Attempts to use ceramic as a structural member have visualized the ceramic primarily as a substitute for the typically well-known metal counterpart. The ceramic was typically used as a monolithic solid piece, with cast in place passages and openings, including passages to receive liquid fuel injectors or electrical igniters (see U.S. Pat. No. 4,508,066 and Japanese Pat. No. 210341).
A unitary ceramic head is very difficult to fabricate and inhibits the ceramic molding technique to that which is more expensive and time consuming. Moreover, solid ceramic heads permit some undesirable heat transfer between the exhaust and intake passages, and some undesirable heat transfer to the fuel injectors.
It would be desirable if a ceramic head could be designed or built from simple geometric blocks or plates with some means providing an air gap or separation between such parts to facilitate insulation of heat transfer between the gas and fluid passages.